Supratentorial white matter tracts

Cerebral white matter has been studied for over 2000 years. The first description of white matter tracts (WMTs) was made by Galen in ad 100. These studies were based on postmortem dissection techniques, but newer technology allows the study of these tracts based on the directional water diffusion along axonal projections to provide in vivo information. These tracts can be classified into three general fiber categories depending on the areas that these WMTs connect-projection fibers, commissural fibers, and association fibers. Projection fibers are those that connect cortical areas with lower subcortical and spinal regions. The most iconic projection pathway is the corticospinal tract, which is the major contributor to voluntary movement as it runs from the cortex and descends into the spinal cord. Commissural fibers are those that connect areas between the two hemispheres. The most iconic commissural pathway is the corpus callosum, which plays a major role in higher order cognitive functions. Association fibers are those that connect areas within the ipsilateral hemisphere. These bundles include the superior, middle, and inferior longitudinal fasciculi; the arcuate fasciculus; the inferior fronto-occipital fasciculus; and the optic radiations; among others. These fibers play a major role in language and vision. Having a complete understanding of these tracts is essential for neurosurgery, and these WMTs will be reviewed in this chapter.